Maintenance Fluid Calculator

Maintenance fluids replace the water a person loses each day through urine, sweat, breathing and stool when they cannot drink normally. The Holliday-Segar method, published in 1957 and still taught worldwide, links those needs to body weight: 100 mL per kg for the first 10 kg, 50 mL per kg for the next 10 kg and 20 mL per kg for every kg above 20. Its hourly shortcut is the familiar 4-2-1 rule.

Enter a weight in kilograms or pounds to see the 24-hour volume, the 4-2-1 hourly infusion rate, and the daily volume spread evenly over 24 hours. It is designed for nursing, medical and paramedic students and for clinicians double-checking a calculation — especially in paediatrics, where the method originated.

These are maintenance figures only. They do not include deficits from dehydration, ongoing losses, or restrictions for heart, kidney or brain conditions, and they say nothing about which fluid to use. Adult guidance such as NICE suggests roughly 25–30 mL/kg/day, so the formula can overestimate for heavier adults. Always follow local protocols and clinical judgement.

Holliday and Segar based maintenance water needs on typical energy expenditure: about 100 kcal/kg/day for the first 10 kg of body weight, 50 kcal/kg/day for the next 10 kg and 20 kcal/kg/day beyond that, with roughly 1 mL of water needed per kcal. Summing the three weight bands gives the daily volume.

The 4-2-1 rule is the hourly version (4, 2 and 1 mL/kg/h for the same bands). Because 4-2-1 was rounded for convenience, 24 hours at that rate differs slightly from the daily figure: it is a little lower up to 35 kg (65 mL/h versus 66.7 mL/h at 25 kg) and a little higher above 35 kg (110 mL/h versus 104.2 mL/h at 70 kg). Weights entered in pounds are converted with 1 kg = 2.2046 lb.